A sensitive fluorometric assay for the simultaneous estimation of pepsin and pepsinogen in gastric mucosa.

An assay for pepsin has been developed based on the fluorometric measurement of trichloroacetic acid-soluble peptides released from casein at pH 5.3. The increase in relative fluorescence was most sensitive in the range 10-50 micrograms pepsin/l and casein hydrolysis was not affected by the addition of up to a 1000-fold molar excess of pepsinogen. This assay has been used to measure the free and total acid proteinase content of biopsies (less than 5 mg) from different areas of the gastric mucosa of rat and man. Interference by the major lysosomal acid hydrolase, cathepsin D, could be eliminated by the differential stability of pepsin and cathepsin D at acid and neutral pH. The free acid proteinase activity of biopsies from the corpus were almost identical in these species whereas the total acid proteinase activity was approximately 5-fold greater in man.